Recent planer antennas for microwaves or millimeter wavelengths have an electric feed-through system configured as a triplate transmission line to provide a highly efficient characteristic, as a prevailing trend. Planer antennas of such a triplate line feed-through system are adapted to synthesize power fed from antenna elements through the triplate transmission line, and in most cases they have, at an interconnect between a final end that outputs synthesized power and an RF signal processing circuit, a triplate line-to-waveguide transducer implementing easy assembly and high connection integrity.
FIGS. 1(a) and 1(b) illustrate, as a part of the background, a configuration of such a triplate line-to-waveguide transducer (refer e.g. to Japanese Utility Model Registration Application Laid-Open Publication No. 06-070305 and Japanese Patent Application Laid-Open Publication No. 2004-215050). In the conventional configuration, in order for the conversion for waveguide system to be facilitated with a small loss, there was a triplate transmission line made up by: a film substrate 4 {FIG. 1(b)} formed with a strip line conductor 3, and laminated over a surface of a ground conductor 1 {FIG. 1(b)}, with a dielectric substrate 2a {FIG. 1(b)} in between; and an upper ground conductor 5 laminated over a surface of the film substrate, with another dielectric substrate 2b {FIG. 1(b)} in between.
Moreover, for connection of such the circuit system to an input portion of a waveguide 6 {FIG. 1(b)}, the ground conductor 1 includes a through hole with dimensions substantially equal to cavity dimensions of the waveguide 6. Further, the film substrate 4 was held by a metallic spacer 7a {FIG. 1(b)} with an even thickness to the dielectric substrate 2a, and another metallic spacer 7b {FIG. 1(b)} with substantially equal dimensions to that metallic spacer 7a, with the film substrate in between, and this metallic spacer 7b had an upper ground conductor 5 arranged thereon. The strip line conductor 3 formed on the film substrate 4 had a square resonant patch pattern 8 {FIG. 1(a)} formed on an area corresponding to a transducer end of the waveguide 6. The square resonant patch pattern 8 had a center position thereof coincident with a center position of cavity dimensions of the waveguide 6. The triplate line-to-waveguide transducer was thus made up.
As illustrated in FIG. 1(a), the square resonant patch pattern 8 had a dimension L1 in a direction in which the line was connected, and a dimension L2 in a direction perpendicular to the direction of line connection, as a prescribed dimension, permitting implementation of the triplate line-to-waveguide transducer with a low-loss characteristic over a wide bandwidth within a desirable range of frequencies.
In the conventional configuration of triplate line-to-waveguide transducer illustrated in FIG. 1, the square resonant patch pattern 8 had dimensions thereof restricted by cavity wall dimensions of the metallic spacers 7a and 7b, with a resultant restriction to the lower limit of resonance frequency, as an issue.